Looks like one of the grapes - Vitis sp.
hortster

Might be a porcelain berry.

... the sticking to the surface of the fence would pretty much have to make it a Parthenocissus. Grapes and porcelain berry are related but climb via twining stems and tendrils only.

Is it indeed attached to the fence with tendrils? Any chance of getting a picture of the stem and any tendrils?
hortster

It's pouring rain now, but I'll try to get another picture of the stem tomorrow. This is another shot I took earlier today. The leaves start out small and round and grow to about 3" across.
{{gwi:352127}}

Definitely a climber and not a grape.
hortster

Looks like the young growth of Boston Ivy, Parthenocissus tricuspidata. Foliage is highly variable on this plant.